By Sandee LaMotte, CNN
“We’ve known for a while that as the belly size gets larger, the memory centers in the brain get smaller,” said Alzheimer’s disease researcher Dr. Richard Isaacson, a preventive neurologist at the Institute for Neurodegenerative Diseases of Florida.
“This study shows a brain imaging marker of neuroinflammation which I had not seen before,” said Isaacson, who was not involved in the new study. “The brain imaging links the belly fat, or visceral fat, to the brain dysfunction through an inflammatory cascade.”
The study found individuals in their 40s and 50s with a greater amount of hidden belly fat “had a higher amount of an abnormal protein called amyloid in a part of the brain that we know is one of the earliest places where Alzheimer’s occurs,” said senior author Dr. Cyrus Raji, associate professor of radiology at Washington University School of Medicine in St. Louis.
Beta amyloid plaques in the brain are one of the hallmark signals of Alzheimer’s, along with tangles of a protein called tau. Amyloid plaques typically appear first, with tau tangles arriving later as the disease progresses.
“There’s a sex difference, as well, where the men had a higher relationship between their belly fat and amyloid than women,” Raji said. “The reason that’s important is because men have more visceral fat than women.”
The study also found a relationship between deep belly fat and brain atrophy, or a wasting away of gray matter, in a part of the brain’s memory center called the hippocampus.
“That’s important because brain atrophy is another biomarker of Alzheimer’s disease,” Raji said.
The brain’s gray matter contains the majority of brain cells that tell the body what to do. White matter is made up of fibers, typically distributed into bundles called tracts, which form connections between brain cells and the rest of the nervous system.
“We also found that the individuals with higher amounts of visceral fat tend to have more inflammation in widespread white matter tracks in the brain,” said lead author Dr. Mahsa Dolatshahi, a postdoctoral research fellow at Washington University School of Medicine.
Without a functional white matter highway, the brain cannot adequately communicate with different parts of the brain and the body.
‘Pushing the envelope’
Published as a pilot study in the journal of Aging and Disease in August, Raji and his team originally imaged the brains and bellies of 32 adults ages 40 to 60. The team kept adding participants and are now presenting information on an additional 20 people — 52 total — at the Radiology Society of North America’s 2023 conference on Monday.
As more people were added to the study, details of how inflammation from belly fat on the parts of the brain where Alzheimer’s originates came into focus. The brain changes they found were modest, but significant, Raji said.
“The reason we’ve shown very subtle effects is because we’re looking at midlife — people in their 40s and 50s — while earlier studies looked at people in their 60s and 70s,” he said. “These are people who, if they do develop Alzheimer’s disease, it won’t happen for another 20 or 25 more years.
“So, we’re really pushing the envelope of how early we can detect some of the kind of subtlest manifestations of abnormalities that can be related to Alzheimer’s pathology,” Raji added. “By identifying this pathological link to visceral fat, there are ways we can potentially intervene in this population.”
Visceral fat and inflammation
When we think of fat, most of us think of subcutaneous fat, the type you can pinch under your skin or along your waistline. Subcutaneous fat typically makes up 90% of the body, according to the Cleveland Clinic.
Visceral fat can’t be poked, prodded or pinched. Visceral fat hides behind the abdominal muscles, deep in the belly, wrapping itself around vital organs. Both types secrete hormones and other molecules, but experts say visceral fat is more metabolically active, sending signals that can trigger insulin resistance and other health issues.
“Subcutaneous fat is typically not associated with insulin resistance,” Isaacson said. “The higher the visceral fat level, however, the more a person has insulin resistance that causes inflammation in the body and the brain.”
Insulin resistance occurs when cells in the body don’t respond well to insulin, a hormone essential for regulating blood sugar levels. The condition often leads to diabetes and a host of other chronic diseases.
“We’ve hypothesized inflammation in the fat cells leads to insulin resistance, and that’s fast-forwarded by visceral fat,” Isaacson said. “Insulin resistance then causes inflammation that fast-forwards amyloid deposition, one of the key markers of Alzheimer’s disease. That’s why people with diabetes have twice the risk of Alzheimer’s disease.”
Expensive full-body MRIs and body scans are the most precise way to measure visceral fat, but many use estimates based on waist circumference or waist size in proportion to height. To measure your waist, the Cleveland Clinic recommends wrapping a flexible tape measure around the waist just above the hips.
“For women, 35 inches (89 centimeters) or more means you’re at risk for health problems stemming from visceral fat. For men, the number is 40 inches (102 centimeters) or more,” the clinic states on its website.
“Regardless of weight, people should find out if they have hidden visceral fat,” Raji said. “It can be totally missed by using body mass index (BMI) or weight on the scale.”
That’s because even thin people can have excess visceral fat. Called “skinny fat” or “TOFI” (thin outside, fat inside), it can happen when a person exercises but has a poor diet, and to certain ethnic groups. Asians, for example, have more visceral fat than Black, White or Hispanic people.
Visceral fat ‘easier to lose’
There’s good news: Visceral fat responds well to diet and exercise, Raji said. “It is easier to lose visceral fat from diet and exercise than it is to lose subcutaneous fat because visceral fat is more easily metabolized and burned.”
There are multiple things that can target body fat, both from an exercise and nutrition perspective, Isaacson said.
“Eat a healthy diet and exercise on a regular basis, which should include muscle strength training a few times a week, along with fat-burning, less intense cardio for 45 to 60 minutes, several times a week,” he said.
More tips: Eliminate or reduce ultraprocessed foods, cut portion sizes, replace sugary drinks with water, limit processed meats, and reduce meat and high-fat dairy products, such as cheese and butter, which are packed with saturated fats, other experts suggest.
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